Health systems are growing nationwide and large systems dominate the hospital market in the U.S. The geographic breadth of these systems is often the result of so-called cross-market mergers: mergers or acquisitions that involve multiple systems or independent hospitals that do not directly compete in the same geographic markets. Recent economic studies found that cross-market mergers led to price increases and harmed competition, despite not sharing a geographic market. The rise of cross-market mergers has enabled health systems to grow rapidly throughout the country and to leverage significant market power against purchasers of health care that span local geographic markets—a phenomenon we call “system power.” Combining the legal expertise of The Source on Healthcare Price and Competition at UC Hastings and the economic and empirical analysis expertise at the Nicholas C. Petris Center on Health Care Markets and Consumer Welfare in the School of Public Health, UC Berkeley, this project aims to provide policymakers with information, resources, and analysis on cross-market hospital systems and mergers.